The present invention relates to a gear shift mechanism of a motor vehicle change-speed gearbox having a plurality of transmission gears which are shiftable by synchronizer clutches, with respective pairs of wheels being formed from mutually meshing fixed wheels and loose wheels. The transmission gears are shiftable by the simultaneous closing of two synchronizer clutches by sliding sleeves, with the sliding sleeve of one synchronizer clutch cooperating in the shifting of all of the transmission gears.
In the book with the title "Gearboxes", Johannes Looman, Springer Publishers, Berlin, 1988, Page 10, auxiliary transmissions are described which represent a usually two-speed range transmission connected in front of or behind the normal gear shift transmission. These auxiliary transmissions have the purpose of increasing the number of gears and the transmission range of the transmission by means of the multiple utilization of sets of wheels without increasing the overall length of the transmission.
When this type of synchronized gear shift transmission is constructed in such a manner that the transmission gears can be shifted by a simultaneous closing of two synchronizer clutches, the expenditure of forces becomes quite high in the case of a purely manual operation.
It is an object of the invention to provide a gear shift mechanism for a transmission of the above described type which can be manufactured with low expenditures, and in which the manual shifting forces can clearly be reduced.
This and other objects are achieved by the present invention which provides a gear shift mechanism of a motor vehicle change-speed gearbox that has a plurality of transmission gears, with respective pairs of wheels formed from mutually meshing fixed wheels. The mechanism includes synchronizer clutches that have sliding sleeves, the synchronizer clutches being engageable with the pairs of wheels to shift the transmission gears. The transmission gears are shiftable by the simultaneous closing of two synchronizer clutches via the sliding sleeves. The sliding sleeve of a first synchronizer clutch of the plurality of synchronizer clutches cooperates in the shifting of all of the transmission gears. A servo drive is coupled to the first synchronizer clutch and operates this first synchronizer clutch. The other synchronizer clutch of the plurality of synchronizer clutches are manually operable.
When the one synchronizer clutch, which participates in the shifting of all transmission gears, is actuated by a servo drive, the shifting work to be performed by the driver of the vehicle is clearly reduced. The driver must manually operate only one synchronizer clutch and the shifting work to be carried out by the driver is less than in the case of conventional transmission shifting. Only the rotating transmission parts (rotating mass portion approximately 15%) must be synchronized manually. The servo device takes over the synchronizing of the clutch disk (rotating mass portion approximately 85%).
Additional feature with respect to the shifting technique and construction which further develop a relatively simple servo drive are also provided in embodiments of the invention. In principle, it would also be possible to shift all synchronizer clutches by means of a servo drive. However, the manufacturing costs for such a shift mechanism would be much higher because an expensive control circuit would be required for the reciprocal adaptation of these servo drives.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.